Studies of the in vitro response of human tumor cells to hyperthermia alone or to hyperthermia in conjunction with x-irradiation can provide valuable information leading to clinical applications. A number of variables including optimum temperature, duration of treatment, and order of application with other modalities can be investigated quickly with the tumor cells in vitro. Biopsy specimens have been obtained from several human tumors including bladder, pancreatic, breast, stomach, and lung and put in both liquid tissue culture and double layer agar cultures. The response to x-irradiation and hyperthermia will be determined for cells from the initial biopsy specimen. Cells isolated from the initial survival in agar and liquid culture will be examined for variation in hyperthermic response to factors such as pH, hypoxia, nutrient levels, and growth phase. This information could aid in estimating the more sensitive human tumors and in designing of treatment protocols to obtain the best clinical response.